There is an function that only turns off the backlight... this is one of the reasons I use a software solution to turn off my ppc as well as to reset it. The only time that I don't is when the unit locks up.. which forces me to do a manual soft reset.
Check out this utility... it may help resolve your issues. But if you are convinced it is not something you are doing I would make the effort to have Hp look at it.
http://www.pocketpcfreewares.com/en/index.php?soft=833